Painting coastal scenes with watercolour washes

Read the coast before you open the palette

Coastal subjects are seductive and treacherous in equal measure. The light shifts, the tide moves, and the wind dries your paper before you have finished a single wash. Before you squeeze out any paint, stand still for a moment and decide what the painting is actually about. Squint until the detail dissolves and you are left with three or four big shapes: a pale sky, a band of sea, a dark headland, a bright ribbon of surf.

Decide where the horizon sits. Two-thirds sky gives you a breezy, open feeling; two-thirds sea gives you weight and depth, which suits a heavy swell or a harbour wall. Avoid parking the horizon in the middle of the paper, which tends to look indecisive. Make a small pencil thumbnail the size of a matchbox, noting only the lights, the mid-tones and the darks. This takes two minutes and saves twenty.

A lean kit that survives a sea breeze

Outdoor sketching rewards simplicity. Take a 300gsm rough or cold-pressed paper, stretched or taped down with gummed tape onto a rigid board; lightweight paper will cock up the moment you lay a wet wash and never lie flat again. Work at a shallow tilt of around fifteen to twenty degrees so the wash flows downwards without pooling in a puddle.

• A large mop or squirrel brush for washes, plus a rigger or small round for rocks and ropes.
• Two water pots: one clean, one for rinsing. Never swap them.
• A limited palette: French ultramarine, cerulean, raw sienna, burnt sienna and a crimson. That is enough for every sea and sky you will meet.
• A sponge, a roll of kitchen paper, and a plastic card for scraping spray.
• Masking fluid if you like crisp foam trails, but keep it off damp paper and off your best brush.

Wind is your main enemy. Wet washes dry fast at the coast, so mix more paint than you think you need before you start, and work in the shade of a wall or a brolly when you can.

Graded washes for the sky and distance

Load the mop generously and sweep it horizontally across the top of the paper, left to right, then reload and repeat, overlapping the previous stroke along its lower edge. As you descend towards the horizon, charge the brush with plain water or a much weaker mix so the wash gradually loses strength. This is a graded wash, and it is the single most useful thing you can learn for coastal work.

Once a wash begins to lose its sheen, leave it alone. Going back over half-dry paper gives you streaks and blossoms you did not ask for. For clouds, drop a little stronger pigment into the damp wash and let it spread on its own, tipping the board slightly so the soft edges travel. Keep the band just above the horizon pale and faintly warm: this is the haze that tells the eye "distance" more convincingly than any amount of detail.

Building the sea with confident horizontal strokes

Wait until the sky is touch-dry, then lay the sea in horizontal strokes, keeping the brush moving. Mix a sea grey from ultramarine with a touch of burnt sienna, or cerulean knocked back with a whisper of crimson; pure blue looks like a swimming pool. Distant water is lighter, cooler and smoother. As you come forward, strengthen the tone, shorten the strokes and let them break up.

Size and contrast increase towards the viewer. That is how you suggest depth without drawing a single wave. Under dark rocks, pull vertical reflections downwards with a thirsty brush while the surface is still damp, and keep them broken rather than solid. A few long, clean horizontal sweeps at the waterline will do more than fifty fussy marks.

Reserved whites and breaking waves

The brightest thing in a coastal painting should be untouched paper. Plan these whites at the drawing stage: a sparkle on the swell, the crest of a breaker, the foam running up the sand. Masking fluid is useful for fine spray and winding foam trails, but anything broad is better left as dry paper you simply paint around.

When you paint a breaking wave, think in three notes. First the reserved white of the crest, jagged and irregular. Second a soft grey shadow on the underside of the crest and in the trough behind it, laid in while the paper is damp. Third a paler, warmer reflection running towards you across the sand. Never outline a wave, and never paint the foam as a solid block of white paint; it will look like icing.

• Flick clean water into a damp wash and let it dry for soft spray.
• Drag a plastic card or knife blade across damp paper for sharp, flying droplets.
• Lift with a clean damp brush and tissue while the paper is damp but no longer shiny, for a gentle glow.

Knowing when to stop

Save your darkest darks for the end. A crisp edge on a rock, a gull, a figure on the sand or a moored dinghy will anchor the scale and tell the viewer how big everything else is. Then stop, before you explain too much. Lay the painting flat to dry, note the time and the weather on the back, and come back to the same cove on a grey day. Painting the same stretch of coast in different light will teach you more about sea and sky than any new brush ever will.